Spinneret for a co-spun filament within a hollow filament

ABSTRACT

A hollow fiber which contains within the hollow a co-spun hollow or solid filament. The solid filament is formed of polymer that can distribute energy within the hollow fiber while a co-spun hollow inner filament can also act as a vessel for transportation or separation of fluids. Spinnerets for co-spinning such filaments are of one piece construction.

BACKGROUND OF THE INVENTION

This invention concerns hollow fibers, and more particularly, hollowfibers co-spun with a core within the hollow portion of the hollowfilament useful as separation devices or for bioreactor applications andspinnerets for co-spinning such fibers.

Hollow-fiber membrane bioreactors are known and have utility in theproduction of materials from suspended or immobilized enzymes or cellcultures. Cells or enzymes are located within or outside of the hollowfibers with reaction substrates being supplied to the cells or enzymeswhile desired products are removed. Cell cultures encompass aerobic oranaerobic cells as well as photosynthetic plant or bacterial cells. Dueto the compact proportions of a bioreactor, known manual methods ofmanufacturing such membranes are costly and time consuming, particularlywhen dual hollow filaments of extended length and fine diameter areinvolved. Another limiting factor in the efficient operation of abioreactor is the ability to deliver the proper levels of substratesinto the system. These substrates include nutrients for cell growth,cofactors for efficient enzyme function, light for photosyntheticreactions and precursor materials for the desired products. In addition,it is known that various energy sources (electrical, mechanical, light,thermal) can regulate cell growth, enzyme activity, membranepermeability and subsequently have a significant effect on the controlor efficiency of a bioreactor.

SUMMARY OF THE INVENTION

A less costly way has now been devised to manufacture such hollow fibermembranes by co-spinning a hollow-within-a-hollow filament for use inapplications where cells or enzymes are located in either of the annularpassages of the filament with addition of substrates and removal ofproducts occurring through the passages or exterior to the filament. Thecomposition of the membrane walls are selected to facilitate diffusionof materials through the walls as well as allow for efficient attachmentof cells or enzymes if immobilization is desired. Similarly, inaddition, a hollow-within-a-hollow filament could be used as a fluidmembrane device by utilizing the outer annular passage for fluidpassage. This fluid could act as a fluid membrane. Either of the annularpassages can be used to transport thermal energy.

In addition, where the inner or core filament is solid the innerfilament may be a light transmitting fiber or an electrically conductivefiber to conduct light or electrical charges respectively into theannular passage surrounding the solid fiber to regulate activity of thebioreactor or separation process.

A spinneret for the production of such filaments comprises a platehaving upper and lower surfaces connected by a capillary. The capillaryis formed of two concentric annular passages with a plurality ofsupports bridging the annular passages. In one embodimenthollow-within-hollow filaments are formed by coalescing polymer streamsflowing out interrupted arcs formed by bridging the annular passages atthe lower surface of the spinneret. Another embodiment of the spinneretprovides venting to the hollow portions of the inner and outer hollowfilaments and in other embodiments various combinations of venting andcoalescing may be used to provide co-spun dual hollow filaments. In eachcase, the spinneret used for co-spinning such filaments is a one-piecespinneret which does not suffer the disadvantages of known multiple-partspinnerets which are adapted to form hollow fibers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 are side elevation, lower surface and upper surface views,respectively, of the spinneret of this invention.

FIGS. 2A and 3A are enlarged views of a spinneret capillary viewed fromthe lower and upper surfaces, respectively, of the spinneret of FIG. 1.

FIG. 4 is an enlarged cross-sectional view of the capillary of FIG. 3Ataken along line 4--4.

FIG. 5 is an alternate embodiment of a spinneret capillary of thisinvention viewed from the lower surface of the spinneret.

FIG. 6 is an enlarged cross-sectional view of the capillary of FIG. 5taken along the line 6--6.

FIG. 7 is another embodiment of a spinneret capillary of this inventionviewed from the lower surface of the spinneret.

FIG. 8 is a cross-sectional view of the capillary of FIG. 7 taken alongline 8--8.

FIGS. 9 and 11 are further embodiments of spinneret capillaries usefulfor this invention viewed from the lower surface of the spinneret.

FIGS. 10 and 12 are cross-sectional views of FIGS. 9 and 11,respectively, taken along lines 10--10 and 12--12.

FIGS. 13, 14 and 15 are photographs enlarged at 200 to 600× ofcross-sectional views of the filaments of this invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Referring now to FIGS. 1-4, spinneret 20 is adapted to be mounted in afilter pack for supplying one or more polymer compositions to be spuninto a filament. The spinneret 20 is formed from a plate 22 and isprovided with a capillary 24, connecting its upper and lower surfaces26, 28, respectively. The capillary is formed of two concentric annularpassages 30, 32, a central cavity 34 located concentrically withinannular passage 32 and a second cavity 36 located between the annularpassages 30, 32. There are a plurality of supports 38, 39 bridgingannular passages 30, 32, respectively, at angular locations around theannular passages to provide structural integrity to the spinneret. Thesesupports 38, 39 extend partially through the annular passages and areradially aligned at the angular locations. A bore 40 leads from thelower surface 28 of the spinneret through two aligned supports 38, 39 tocavities 34, 36 for the purpose of venting the cavities.

In operation, a molten polymer composition moves initially into recess26a of the upper surface 26 of the spinneret, then it is uniformlydistributed through annular passage 30 to form a hollow filament. At thesame time, another polymer composition is fed to annular passage 32 toform a hollow filament within the hollow filament formed from passage30. As polymer flows out from the exit end of the capillary, a partialvacuum is formed causing a gravity flow of room air through bore 40 tocavities 34, 36 and into the inner and outer hollow filaments.

In another embodiment of the spinneret of this invention as shown inFIGS. 5 and 6 only the cavity 34 of capillary 24' is vented through bore40 (cavity 36 has been eliminated) and the annular passage 30' isbridged at lower surface 28 by members 42 (shown as if revolved to line6--6 in FIG. 6) to provide a segmented orifice at the outlet of passage30. This capillary combines both coalescent spinning of hollow filamentsthrough annular passage 30 and vented spinning of hollow filamentsthrough annular passage 32.

In still another embodiment of the spinneret of this invention shown inFIGS. 7 and 8 only cavity 36 of capillary 24" is vented through bore 40(cavity 34 has been eliminated) and the annular passage 32 is bridged atlower surface 28 by members 44 (shown as if revolved to line 8--8 inFIG. 8) to provide a segmented arc orifice at the outlet of passage 32'.This capillary combines both coalescent spinning through annular passage32 and vented spinning through annular passage 30.

In still another embodiment shown in FIGS. 9-10 both passages 30', 32'of capillary 24'" are adapted for coalescent spinning of dual hollowfilaments by eliminating cavities 34, 36 and bore 40 and providingannular passages 30, 32 with bridging members 42, 44 (both shown as ifrevolved to line 10--10 in FIG. 10) at lower surface 28 to formsegmented arc orifices at the outlet of passages 30, 32.

The embodiment shown in FIGS. 11 and 12 provides for co-spinning acoalesced hollow filament with a solid filament within the hollow. Thesolid filament could be spun from polymers which are electricallyconductive or which have light transmitting characteristics. In thisembodiment the capillary 50 is formed of an annular passage 52 separatedfrom and surrounding a central bore 54. Supports 56 bridge annularpassage 52 and extend partially through the passage while members 57(shown as if revolved to line 12--12 in FIG. 12) provide a segmentedorifice at the exit of passage 52 by bridging the passage at surface 58.Central bore 54 terminates at the lower surface 58 of the spinneret in acruciform-shaped orifice 60. Different polymer compositions are fed topassage 52 and central bore 54. A hollow filament is formed from passage52 with its solid cruciformed core being formed from polymer extrudedfrom orifice 60.

While supports 38 and 39 have been illustrated and described asextending partially through annular passages 30,32, it should beunderstood that supports 38,39 could extend completely through thepassages.

EXAMPLE 1

This example describes the co-spinning of a hollow-within-a-hollowbicomponent fiber. The spinneret used was a 6-capillary double-ventedspinneret of the type shown in FIGS. 1-4. The spinneret capillaries hadthe following dimensions:

Outer annular polymer passage 30

i.d.=0.200 in.

width=0.005 in.

depth=0.020 in.

Inner annular polymer passage 32

i.d.=0.096 in.

width=0.005 in.

depth=0.020 in.

The inner and outer hollow-filaments were co-spun from Hercules, Inc.Textile Grade 6523F polypropylene (melt index=3-4.5) and polyethyleneterephthalate (LRV=21.4), respectively. The polyethylene terephthalatecontained 0.3% TiO2 as a delusterant. The two polymers were meltedseparately in heated zone screw melters to a temperature of 275° C. andthen extruded through the spinneret which was maintained at 268° C. Thepolypropylene polymer forming the inner-filament was metered at a rateof 0.9 g/min/passage and the polyethylene terephthalate polymer formingthe outer-filament was metered at a rate of 3.3 g/min/passage.

After the filaments were extruded from the spinneret, they were quenchedwith room temperature cross-flow air and passed over a contact finishroll where a spin-finish (a 10% solution of an akylstearate esterlubricant emulsified with Aerosol® OT and Merpol® 1452) was applied toeffect cohesion in the multi-filament bundle. The filaments were thenbrought together using convergence guides and wound-up onto a bobbin at300 mpm. The filament was cut into thin sections and examined underlight microscopy at a magnification of 200× and found to be ahollow-within-a-hollow filament as shown in FIG. 13. The inner hollowfilament 60 was free (i.e., not fused) from the inner surface 62 of theouter hollow filament 64.

EXAMPLE 2

This example describes the co-spinning of an electrically conductivesolid-filament within a hollow-filament. The spinneret used was a6-capillary spinneret having a polymer coalescing outer ring of the typeshown in FIGS. 11 and 12. Three of the capillaries contained atrilobally-shaped inner polymer orifice and three of the capillariescontained a cruciform-shaped inner polymer orifice. The spinneretcapillaries had the following dimensions:

Outer annular polymer passage 52

o.d.=0.189 in.

width=0.006 in.

bridge length=0.011 in.

depth=0.025 in.

Inner polymer orifice 60

arm length=0.0035 in.

slot width=0.003 in.

depth=0.012 in.

The inner filament consisted of a mixture of electrically conductivecarbon black in polyethylene and was co-spun with a polyethyleneterephthalate (LRV=23.5) outer filament. The carbon black was 28% byweight of the inner filament. The polymers for the inner and outerfilaments were melted separately in heated zone screw melters to atemperature of 270° C. and extruded through the spinneret which wasmaintained at 268° C. The carbon black/polyethylene polymer forming theinner-filament was metered at a rate of 0.83 g/min/orifice and thepolyethylene terephth poloymer forming the outer filament was metered ata rate of 3.85 g/min/passage.

After the filaments were extruded from the spinneret, they were quenchedwith room temperature cross-flow air and passed over a contact finishroll where a spin-finish as per Example 1 was applied to effect cohesionin the multi-filament bundle. The filaments were then brought togetherusing convergence guides and wound-up onto a bobbin at 1200 mpm. Thefilaments were cut and the cut end examined using scanning electronmicroscopy at a magnification of 500× and found to be a solid within ahollow filament as shown in FIG. 14. The inner filament 70 was free(i.e., not fused) from the inner surface 72 of the hollow filament 74.

EXAMPLE 3

This example describes the co-spinning of a relatively clearsolid-filament within a hollow-filament. The spinneret used was the sameas described in Example 2.

The inner and outer filaments were co-spun from polypropylene (meltindex=3-4.5) and polyethylene terephthalate (LRV=23.5), respectively.The polyethylene terephthalate contained 0.3% TiO2 as a delusterant. Thetwo polymers were melted separately in heated zone screw melters to atemperature of 280° C. and then extruded through a spinneret which wasmaintained at 265° C. The polypropylene polymer forming theinner-filament was metered at a rate of 4.2 g/min/orifice and thepolyethylene terephthalate polymer forming the outer-filament wasmetered at a rate of 4.95 g/min/passage.

After the filaments were extruded from the spinneret, they were quenchedwith room temperature cross-flow air and passed over a contact finishroll where a spin-finish as per Example 1 was applied to effect cohesionin the multi-filament bundle. The filaments were then brought togetherusing convergence guides and wound-up onto a bobbin at 300 mpm. Thefilament was cut into thin sections and examined using light microscopyat a magnification of 600× and found to be a solid within a hollowfilament as shown in FIG. 15. The solid filament 80 was free (i.e., notfused) from the inner surface 82 of the hollow filament 84.

I claim:
 1. A one piece spinneret for the production of a hollowfilament containing within itself a cospun filament comprising: a platehaving upper and lower surfaces connected by a capillary, said capillarybeing formed of two concentric annular passages, a central cavityconcentrically located within the inner annular passage, and a secondcavity located between said annular passages, a plurality of supportsbridging said annular passages at angular locations around said annularpassages, said supports extending through said annular passages andbeing radially aligned at said angular locations and a bore leading fromsaid lower surface through two aligned bridge members to said cavities.2. A one piece spinneret for the production of a hollow filamentcontaining within itself a cospun filament comprising: a plate havingupper and lower surfaces connected by a capillary, said capillary beingformed of two concentric annular passages, a central cavityconcentrically located within the inner annular passage, a plurality ofsupports bridging said annular passages at angular locations around saidannular passages, said supports extending through said annular passagesand being radially aligned at said angular locations and a bore leadingfrom said lower surface through two aligned support members to saidcentral cavity; and a plurality of members bridging the outer annularpassage at said lower surface of the spinneret.
 3. A one piece spinneretfor the production of hollow filaments comprising: a plate having upperand lower surfaces connected by a capillary, said capillary being formedof two concentric annular passages, a plurality of supports bridgingsaid annular passages at angular locations around said annular passages,said supports extending through said annular passages and a plurality ofmembers bridging the outer and inner annular passages at said lowersurface of the spinneret.
 4. A one piece spinneret for the production ofhollow filaments comprising: a plate having upper and lower surfacesconnected by a capillary, said capillary being formed of two concentricannular passages, a cavity located between said annular passages, aplurality of supports bridging said annular passages at angularlocations around said annular passages, said supports extending throughsaid annular passages and a bore leading from said lower surface througha support member to said annular cavity; and a plurality of membersbridging the inner annular passage at said lower surface of thespinneret.